posix: retry on symlink race in checklink

Multiple threads might attempt to check links with the same temporary
name. This would cause one side to get an EEXIST error and wrongly
fail the support check. Here, we simply retry if our temporary name
exists.

mercurial/posix.py

@@ -1,649 +1,653 b''
 # posix.py - Posix utility function implementations for Mercurial
 #
 #  Copyright 2005-2009 Matt Mackall <[e-mail]> and others
 #
 # This software may be used and distributed according to the terms of the
 # GNU General Public License version 2 or any later version.
 
 from __future__ import absolute_import
 
 import errno
 import fcntl
 import getpass
 import grp
 import os
 import pwd
 import re
 import select
 import socket
 import stat
 import sys
 import tempfile
 import unicodedata
 
 from .i18n import _
 from . import (
     encoding,
 )
 
 posixfile = open
 normpath = os.path.normpath
 samestat = os.path.samestat
 oslink = os.link
 unlink = os.unlink
 rename = os.rename
 removedirs = os.removedirs
 expandglobs = False
 
 umask = os.umask(0)
 os.umask(umask)
 
 def split(p):
     '''Same as posixpath.split, but faster
 
     >>> import posixpath
     >>> for f in ['/absolute/path/to/file',
     ...           'relative/path/to/file',
     ...           'file_alone',
     ...           'path/to/directory/',
     ...           '/multiple/path//separators',
     ...           '/file_at_root',
     ...           '///multiple_leading_separators_at_root',
     ...           '']:
     ...     assert split(f) == posixpath.split(f), f
     '''
     ht = p.rsplit('/', 1)
     if len(ht) == 1:
         return '', p
     nh = ht[0].rstrip('/')
     if nh:
         return nh, ht[1]
     return ht[0] + '/', ht[1]
 
 def openhardlinks():
     '''return true if it is safe to hold open file handles to hardlinks'''
     return True
 
 def nlinks(name):
     '''return number of hardlinks for the given file'''
     return os.lstat(name).st_nlink
 
 def parsepatchoutput(output_line):
     """parses the output produced by patch and returns the filename"""
     pf = output_line[14:]
     if os.sys.platform == 'OpenVMS':
         if pf[0] == '`':
             pf = pf[1:-1] # Remove the quotes
     else:
         if pf.startswith("'") and pf.endswith("'") and " " in pf:
             pf = pf[1:-1] # Remove the quotes
     return pf
 
 def sshargs(sshcmd, host, user, port):
     '''Build argument list for ssh'''
     args = user and ("%s@%s" % (user, host)) or host
     return port and ("%s -p %s" % (args, port)) or args
 
 def isexec(f):
     """check whether a file is executable"""
     return (os.lstat(f).st_mode & 0o100 != 0)
 
 def setflags(f, l, x):
     s = os.lstat(f).st_mode
     if l:
         if not stat.S_ISLNK(s):
             # switch file to link
             fp = open(f)
             data = fp.read()
             fp.close()
             os.unlink(f)
             try:
                 os.symlink(data, f)
             except OSError:
                 # failed to make a link, rewrite file
                 fp = open(f, "w")
                 fp.write(data)
                 fp.close()
         # no chmod needed at this point
         return
     if stat.S_ISLNK(s):
         # switch link to file
         data = os.readlink(f)
         os.unlink(f)
         fp = open(f, "w")
         fp.write(data)
         fp.close()
         s = 0o666 & ~umask # avoid restatting for chmod
 
     sx = s & 0o100
     if x and not sx:
         # Turn on +x for every +r bit when making a file executable
         # and obey umask.
         os.chmod(f, s | (s & 0o444) >> 2 & ~umask)
     elif not x and sx:
         # Turn off all +x bits
         os.chmod(f, s & 0o666)
 
 def copymode(src, dst, mode=None):
     '''Copy the file mode from the file at path src to dst.
     If src doesn't exist, we're using mode instead. If mode is None, we're
     using umask.'''
     try:
         st_mode = os.lstat(src).st_mode & 0o777
     except OSError as inst:
         if inst.errno != errno.ENOENT:
             raise
         st_mode = mode
         if st_mode is None:
             st_mode = ~umask
         st_mode &= 0o666
     os.chmod(dst, st_mode)
 
 def checkexec(path):
     """
     Check whether the given path is on a filesystem with UNIX-like exec flags
 
     Requires a directory (like /foo/.hg)
     """
 
     # VFAT on some Linux versions can flip mode but it doesn't persist
     # a FS remount. Frequently we can detect it if files are created
     # with exec bit on.
 
     try:
         EXECFLAGS = stat.S_IXUSR | stat.S_IXGRP | stat.S_IXOTH
         fh, fn = tempfile.mkstemp(dir=path, prefix='hg-checkexec-')
         try:
             os.close(fh)
             m = os.stat(fn).st_mode & 0o777
             new_file_has_exec = m & EXECFLAGS
             os.chmod(fn, m ^ EXECFLAGS)
             exec_flags_cannot_flip = ((os.stat(fn).st_mode & 0o777) == m)
         finally:
             os.unlink(fn)
     except (IOError, OSError):
         # we don't care, the user probably won't be able to commit anyway
         return False
     return not (new_file_has_exec or exec_flags_cannot_flip)
 
 def checklink(path):
     """check whether the given path is on a symlink-capable filesystem"""
     # mktemp is not racy because symlink creation will fail if the
     # file already exists
-    name = tempfile.mktemp(dir=path, prefix='hg-checklink-')
-    try:
-        fd = tempfile.NamedTemporaryFile(dir=path, prefix='hg-checklink-')
+    while True:
+        name = tempfile.mktemp(dir=path, prefix='hg-checklink-')
         try:
-            os.symlink(os.path.basename(fd.name), name)
-            os.unlink(name)
-            return True
-        finally:
-            fd.close()
-    except AttributeError:
-        return False
-    except OSError as inst:
-        # sshfs might report failure while successfully creating the link
-        if inst[0] == errno.EIO and os.path.exists(name):
-            os.unlink(name)
-        return False
+            fd = tempfile.NamedTemporaryFile(dir=path, prefix='hg-checklink-')
+            try:
+                os.symlink(os.path.basename(fd.name), name)
+                os.unlink(name)
+                return True
+            except OSError as inst:
+                # link creation might race, try again
+                if inst[0] == errno.EEXIST:
+                    continue
+                # sshfs might report failure while successfully creating the link
+                if inst[0] == errno.EIO and os.path.exists(name):
+                    os.unlink(name)
+                return False
+            finally:
+                fd.close()
+        except AttributeError:
+            return False
 
 def checkosfilename(path):
     '''Check that the base-relative path is a valid filename on this platform.
     Returns None if the path is ok, or a UI string describing the problem.'''
     pass # on posix platforms, every path is ok
 
 def setbinary(fd):
     pass
 
 def pconvert(path):
     return path
 
 def localpath(path):
     return path
 
 def samefile(fpath1, fpath2):
     """Returns whether path1 and path2 refer to the same file. This is only
     guaranteed to work for files, not directories."""
     return os.path.samefile(fpath1, fpath2)
 
 def samedevice(fpath1, fpath2):
     """Returns whether fpath1 and fpath2 are on the same device. This is only
     guaranteed to work for files, not directories."""
     st1 = os.lstat(fpath1)
     st2 = os.lstat(fpath2)
     return st1.st_dev == st2.st_dev
 
 # os.path.normcase is a no-op, which doesn't help us on non-native filesystems
 def normcase(path):
     return path.lower()
 
 # what normcase does to ASCII strings
 normcasespec = encoding.normcasespecs.lower
 # fallback normcase function for non-ASCII strings
 normcasefallback = normcase
 
 if sys.platform == 'darwin':
 
     def normcase(path):
         '''
         Normalize a filename for OS X-compatible comparison:
         - escape-encode invalid characters
         - decompose to NFD
         - lowercase
         - omit ignored characters [200c-200f, 202a-202e, 206a-206f,feff]
 
         >>> normcase('UPPER')
         'upper'
         >>> normcase('Caf\xc3\xa9')
         'cafe\\xcc\\x81'
         >>> normcase('\xc3\x89')
         'e\\xcc\\x81'
         >>> normcase('\xb8\xca\xc3\xca\xbe\xc8.JPG') # issue3918
         '%b8%ca%c3\\xca\\xbe%c8.jpg'
         '''
 
         try:
             return encoding.asciilower(path)  # exception for non-ASCII
         except UnicodeDecodeError:
             return normcasefallback(path)
 
     normcasespec = encoding.normcasespecs.lower
 
     def normcasefallback(path):
         try:
             u = path.decode('utf-8')
         except UnicodeDecodeError:
             # OS X percent-encodes any bytes that aren't valid utf-8
             s = ''
             g = ''
             l = 0
             for c in path:
                 o = ord(c)
                 if l and o < 128 or o >= 192:
                     # we want a continuation byte, but didn't get one
                     s += ''.join(["%%%02X" % ord(x) for x in g])
                     g = ''
                     l = 0
                 if l == 0 and o < 128:
                     # ascii
                     s += c
                 elif l == 0 and 194 <= o < 245:
                     # valid leading bytes
                     if o < 224:
                         l = 1
                     elif o < 240:
                         l = 2
                     else:
                         l = 3
                     g = c
                 elif l > 0 and 128 <= o < 192:
                     # valid continuations
                     g += c
                     l -= 1
                     if not l:
                         s += g
                         g = ''
                 else:
                     # invalid
                     s += "%%%02X" % o
 
             # any remaining partial characters
             s += ''.join(["%%%02X" % ord(x) for x in g])
             u = s.decode('utf-8')
 
         # Decompose then lowercase (HFS+ technote specifies lower)
         enc = unicodedata.normalize('NFD', u).lower().encode('utf-8')
         # drop HFS+ ignored characters
         return encoding.hfsignoreclean(enc)
 
 if sys.platform == 'cygwin':
     # workaround for cygwin, in which mount point part of path is
     # treated as case sensitive, even though underlying NTFS is case
     # insensitive.
 
     # default mount points
     cygwinmountpoints = sorted([
             "/usr/bin",
             "/usr/lib",
             "/cygdrive",
             ], reverse=True)
 
     # use upper-ing as normcase as same as NTFS workaround
     def normcase(path):
         pathlen = len(path)
         if (pathlen == 0) or (path[0] != os.sep):
             # treat as relative
             return encoding.upper(path)
 
         # to preserve case of mountpoint part
         for mp in cygwinmountpoints:
             if not path.startswith(mp):
                 continue
 
             mplen = len(mp)
             if mplen == pathlen: # mount point itself
                 return mp
             if path[mplen] == os.sep:
                 return mp + encoding.upper(path[mplen:])
 
         return encoding.upper(path)
 
     normcasespec = encoding.normcasespecs.other
     normcasefallback = normcase
 
     # Cygwin translates native ACLs to POSIX permissions,
     # but these translations are not supported by native
     # tools, so the exec bit tends to be set erroneously.
     # Therefore, disable executable bit access on Cygwin.
     def checkexec(path):
         return False
 
     # Similarly, Cygwin's symlink emulation is likely to create
     # problems when Mercurial is used from both Cygwin and native
     # Windows, with other native tools, or on shared volumes
     def checklink(path):
         return False
 
 _needsshellquote = None
 def shellquote(s):
     if os.sys.platform == 'OpenVMS':
         return '"%s"' % s
     global _needsshellquote
     if _needsshellquote is None:
         _needsshellquote = re.compile(r'[^a-zA-Z0-9._/+-]').search
     if s and not _needsshellquote(s):
         # "s" shouldn't have to be quoted
         return s
     else:
         return "'%s'" % s.replace("'", "'\\''")
 
 def quotecommand(cmd):
     return cmd
 
 def popen(command, mode='r'):
     return os.popen(command, mode)
 
 def testpid(pid):
     '''return False if pid dead, True if running or not sure'''
     if os.sys.platform == 'OpenVMS':
         return True
     try:
         os.kill(pid, 0)
         return True
     except OSError as inst:
         return inst.errno != errno.ESRCH
 
 def explainexit(code):
     """return a 2-tuple (desc, code) describing a subprocess status
     (codes from kill are negative - not os.system/wait encoding)"""
     if code >= 0:
         return _("exited with status %d") % code, code
     return _("killed by signal %d") % -code, -code
 
 def isowner(st):
     """Return True if the stat object st is from the current user."""
     return st.st_uid == os.getuid()
 
 def findexe(command):
     '''Find executable for command searching like which does.
     If command is a basename then PATH is searched for command.
     PATH isn't searched if command is an absolute or relative path.
     If command isn't found None is returned.'''
     if sys.platform == 'OpenVMS':
         return command
 
     def findexisting(executable):
         'Will return executable if existing file'
         if os.path.isfile(executable) and os.access(executable, os.X_OK):
             return executable
         return None
 
     if os.sep in command:
         return findexisting(command)
 
     if sys.platform == 'plan9':
         return findexisting(os.path.join('/bin', command))
 
     for path in os.environ.get('PATH', '').split(os.pathsep):
         executable = findexisting(os.path.join(path, command))
         if executable is not None:
             return executable
     return None
 
 def setsignalhandler():
     pass
 
 _wantedkinds = set([stat.S_IFREG, stat.S_IFLNK])
 
 def statfiles(files):
     '''Stat each file in files. Yield each stat, or None if a file does not
     exist or has a type we don't care about.'''
     lstat = os.lstat
     getkind = stat.S_IFMT
     for nf in files:
         try:
             st = lstat(nf)
             if getkind(st.st_mode) not in _wantedkinds:
                 st = None
         except OSError as err:
             if err.errno not in (errno.ENOENT, errno.ENOTDIR):
                 raise
             st = None
         yield st
 
 def getuser():
     '''return name of current user'''
     return getpass.getuser()
 
 def username(uid=None):
     """Return the name of the user with the given uid.
 
     If uid is None, return the name of the current user."""
 
     if uid is None:
         uid = os.getuid()
     try:
         return pwd.getpwuid(uid)[0]
     except KeyError:
         return str(uid)
 
 def groupname(gid=None):
     """Return the name of the group with the given gid.
 
     If gid is None, return the name of the current group."""
 
     if gid is None:
         gid = os.getgid()
     try:
         return grp.getgrgid(gid)[0]
     except KeyError:
         return str(gid)
 
 def groupmembers(name):
     """Return the list of members of the group with the given
     name, KeyError if the group does not exist.
     """
     return list(grp.getgrnam(name).gr_mem)
 
 def spawndetached(args):
     return os.spawnvp(os.P_NOWAIT | getattr(os, 'P_DETACH', 0),
                       args[0], args)
 
 def gethgcmd():
     return sys.argv[:1]
 
 def termwidth():
     try:
         import array
         import termios
         for dev in (sys.stderr, sys.stdout, sys.stdin):
             try:
                 try:
                     fd = dev.fileno()
                 except AttributeError:
                     continue
                 if not os.isatty(fd):
                     continue
                 try:
                     arri = fcntl.ioctl(fd, termios.TIOCGWINSZ, '\0' * 8)
                     width = array.array('h', arri)[1]
                     if width > 0:
                         return width
                 except AttributeError:
                     pass
             except ValueError:
                 pass
             except IOError as e:
                 if e[0] == errno.EINVAL:
                     pass
                 else:
                     raise
     except ImportError:
         pass
     return 80
 
 def makedir(path, notindexed):
     os.mkdir(path)
 
 def unlinkpath(f, ignoremissing=False):
     """unlink and remove the directory if it is empty"""
     try:
         os.unlink(f)
     except OSError as e:
         if not (ignoremissing and e.errno == errno.ENOENT):
             raise
     # try removing directories that might now be empty
     try:
         os.removedirs(os.path.dirname(f))
     except OSError:
         pass
 
 def lookupreg(key, name=None, scope=None):
     return None
 
 def hidewindow():
     """Hide current shell window.
 
     Used to hide the window opened when starting asynchronous
     child process under Windows, unneeded on other systems.
     """
     pass
 
 class cachestat(object):
     def __init__(self, path):
         self.stat = os.stat(path)
 
     def cacheable(self):
         return bool(self.stat.st_ino)
 
     __hash__ = object.__hash__
 
     def __eq__(self, other):
         try:
             # Only dev, ino, size, mtime and atime are likely to change. Out
             # of these, we shouldn't compare atime but should compare the
             # rest. However, one of the other fields changing indicates
             # something fishy going on, so return False if anything but atime
             # changes.
             return (self.stat.st_mode == other.stat.st_mode and
                     self.stat.st_ino == other.stat.st_ino and
                     self.stat.st_dev == other.stat.st_dev and
                     self.stat.st_nlink == other.stat.st_nlink and
                     self.stat.st_uid == other.stat.st_uid and
                     self.stat.st_gid == other.stat.st_gid and
                     self.stat.st_size == other.stat.st_size and
                     self.stat.st_mtime == other.stat.st_mtime and
                     self.stat.st_ctime == other.stat.st_ctime)
         except AttributeError:
             return False
 
     def __ne__(self, other):
         return not self == other
 
 def executablepath():
     return None # available on Windows only
 
 class unixdomainserver(socket.socket):
     def __init__(self, join, subsystem):
         '''Create a unix domain socket with the given prefix.'''
         super(unixdomainserver, self).__init__(socket.AF_UNIX)
         sockname = subsystem + '.sock'
         self.realpath = self.path = join(sockname)
         if os.path.islink(self.path):
             if os.path.exists(self.path):
                 self.realpath = os.readlink(self.path)
             else:
                 os.unlink(self.path)
         try:
             self.bind(self.realpath)
         except socket.error as err:
             if err.args[0] == 'AF_UNIX path too long':
                 tmpdir = tempfile.mkdtemp(prefix='hg-%s-' % subsystem)
                 self.realpath = os.path.join(tmpdir, sockname)
                 try:
                     self.bind(self.realpath)
                     os.symlink(self.realpath, self.path)
                 except (OSError, socket.error):
                     self.cleanup()
                     raise
             else:
                 raise
         self.listen(5)
 
     def cleanup(self):
         def okayifmissing(f, path):
             try:
                 f(path)
             except OSError as err:
                 if err.errno != errno.ENOENT:
                     raise
 
         okayifmissing(os.unlink, self.path)
         if self.realpath != self.path:
             okayifmissing(os.unlink, self.realpath)
             okayifmissing(os.rmdir, os.path.dirname(self.realpath))
 
 def statislink(st):
     '''check whether a stat result is a symlink'''
     return st and stat.S_ISLNK(st.st_mode)
 
 def statisexec(st):
     '''check whether a stat result is an executable file'''
     return st and (st.st_mode & 0o100 != 0)
 
 def poll(fds):
     """block until something happens on any file descriptor
 
     This is a generic helper that will check for any activity
     (read, write.  exception) and return the list of touched files.
 
     In unsupported cases, it will raise a NotImplementedError"""
     try:
         res = select.select(fds, fds, fds)
     except ValueError: # out of range file descriptor
         raise NotImplementedError()
     return sorted(list(set(sum(res, []))))
 
 def readpipe(pipe):
     """Read all available data from a pipe."""
     # We can't fstat() a pipe because Linux will always report 0.
     # So, we set the pipe to non-blocking mode and read everything
     # that's available.
     flags = fcntl.fcntl(pipe, fcntl.F_GETFL)
     flags |= os.O_NONBLOCK
     oldflags = fcntl.fcntl(pipe, fcntl.F_SETFL, flags)
 
     try:
         chunks = []
         while True:
             try:
                 s = pipe.read()
                 if not s:
                     break
                 chunks.append(s)
             except IOError:
                 break
 
         return ''.join(chunks)
     finally:
         fcntl.fcntl(pipe, fcntl.F_SETFL, oldflags)